1. Field of the Invention
The present invention relates to a device for feeding toner of a laser beam printer and, more particularly, to a device for feeding toner which is designed to feed a limited amount of toner contained in a toner hopper of a laser beam printer into a developer for image development.
2. Related Art
In laser beam printers, toner feeding device is customarily used as part of a mono-component developer such as disclosed in U.S. Pat. Nos. 4,194,830 for Development Apparatus issued to Ohnuma et al., 5,016,560 for Device For Image Toner Distribution On A Developing Device issued to Asada et al., 5,128,722 for Developing Device Excellent In Toner Transportability issued to Natsuhara et al., and 5,138,385 for Developing Device With Electrically Floating Developing Roller issued to Toyoshi et al., for feeding toner to develop an electrostatic image formed on an image carrier such as a photosensitive drum. Mono-component developers which can be magnetic and non-magnetic are generally simpler and smaller in size and lower in cost, when compared with two-component developers. In principle, a developing roller is set between a photosensitive drum and a toner hopper. A feeding roller which supplies toner to the developing roller and a coating blade is pressed against the developing roller. Rotation of the feeding roller causes toner particles to be transferred to the developing roller so as to form a thin toner layer on the developing roller. As the developing roller is rotated, a single-component toner adheres to the surface of the developing roller by electronic charges between a coating blade and toner particles, and between the developing roller and the toner particles. Then, the toner particles, supported on the developing roller are caused to adhere electrostatically on a photosensitive drum to form an electrostatic latent image.
Contemporary toner hopper generally has a rectangular-shaped feeding opening of a predetermined width as described, for example, in U.S. Pat. Nos. 4,418,643 for Feed Hopper Assembly For Particulate Material And Printer issued to Barto, Jr. et al., 4,548,490 for Toner Feeder System issued to Stirrat et al., 4,594,277 for Toner Supply Control System issued to Maczuszenko et al., and 5,307,128 for Toner Supply Device issued to Murasaki et al., for supplying toner to the developing roller for image development. Such an extended opening of the toner hopper, however, causes a lump of toner around the feeding roller when a large amount of toner is introduced into the developer. When a lump of toner is introduced into the developer, the toner is difficult to agitate and is susceptible to leakage. As a result, the quality of image printing is deteriorated.